Association of neutering with health and welfare of urban free-roaming cat population in Israel, during 2012-2014.

'Trap-Neutering by gonadectomy-Return' (TNR) is currently becoming an accepted method for managing free-roaming cat (FRC) populations, especially in human habitation. However, data regarding its impact on cat welfare are limited. In order to determine the demographic risk factors for FRC morbidity, we followed FRC populations in the city of Rishon LeZion during 2012-2014. Their age status (kitten/adult), contraceptive status (neutered/intact), sex, body-condition-scoring (BCS 1-5/5; 1= emaciation, 5= obesity), skin lesions, and external signs of disabilities and injuries were recorded and analyzed. We fitted a mixed effects generalized linear model to each cat-condition. Overall, 4615 cat-observations were recorded, of which 692 were kittens, 2365 neutered adults and 1445 intact adults. In comparison to intact adults, kittens had a significantly higher prevalence of emaciation (BCS 1; OR of 4.61, CI95% 2.67-7.6, p < 0.001) and severe disability or injury (OR of 3.65, CI95% 1.44-9.25, p = 0.006). Among adult cats, neutered cats had higher prevalence of obesity (BCS 5; OR 30.6, CI95% 10.06-93.09, p < 0.001), lower prevalence of skin lesions (OR of 0.51, CI95% 0.3-0.86, p = 0.011), and close to significant lower prevalence of severe disability or injury (OR of 0.4, CI95% 0.15-1.07, p = 0.068). However, these neutered adults also had a higher prevalence of permanent disability (e.g. anophthalmia, tail or limb absence) (OR of 1.67, CI95% 1.12-2.49, p = 0.012). A higher ratio of neutered FRCs in the geographical surroundings was correlated with a reduced prevalence of emaciated (BCS 1; OR of 0.85 for the increase of 10% in proportion of neutered cats, CI95% 0.74-0.97, p = 0.020) and thin adult cats (BCS 2; OR of 0.94 for the increase of 10% in proportion of neutered cats, CI95% 0.90-0.98, p = 0.010), among both neutered and intact cats. The results suggest that neutering has a favorable effect on FRC health. Such effect can be due to both a direct influence on the neutered cats themselves, as well as to an indirect effect on the general cat population (intact and neutered cats) by reducing competitive behavior of the neutered cats, which may enable other cats to gain additional access to vital resources. A higher prevalence of permanent disability found among the neutered FRCs does not necessarily represent a higher risk of injury but can rather be attributed to their potentially prolonged lifespan.